Noting that it has entered this state after a sustained series of volcanic earthquakes over seven days.
On Sunday, March 22, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported that the Bulusan Volcano in Sorsogon has been raised to under Alert Level 1, which means it is now in the state of a “low-level unrest.”
It also said that the volcano currently has “increased chances of phreatic eruptions.”
According to the bureau, it monitored the first series of volcanic earthquakes that started March 15. Since then, it has recorded a total of four hundred seventy-five (475) volcanic earthquakes.
“Most of these were weak volcano-tectonic earthquakes that are associated with rock fracturing at shallow depths beneath the volcano edifice and are similar in general characteristics to seismicity prior to the June 2022 and April 2025 eruptions,” noted the state volcanologists.
In addition to this, it also shared the ground deformation data from continuous GPS and electronic tilt monitoring indicate that there is “inflation or swelling” of the western and southeastern flank of Bulusan since the last week of January and first week of March 2026, respectively.
Degassing activity from the active vents when visible, it told, has been weak to moderate, consistent with weak volcanic sulfur dioxide (SO2) emission as indicated by below background averages of 91 tonnes/day measured on March 17.
“Overall, these parameters could indicate that shallow hydrothermal processes beneath the volcano are underway that could lead to steam-driven or phreatic eruptions at any of its summit vents,” PHIVOLCS also said.
In light of these developments, the local government units and the civilian population in the areas surrounding the volcano are reminded that entry into the 4-kilometer radius Permanent Danger Zone (PDZ) should be strictly prohibited and that vigilance in the 2-kilometer Extended Danger Zone (EDZ) on the southeast sector should be exercised.
This is due to the possible impact of specific volcanic hazards such as pyroclastic density currents or PDCs, ballistic projectiles, rockfall, avalanches and ashfall on these danger areas.
Communities west of the volcano, meanwhile, have also been advised to prepare for ashfall in case phreatic eruption occurs, with special attention to vulnerable members of the community including the elderly, expecting mothers, infants and those with medical conditions.
PHIVOLCS also instructed the civil aviation authorities to advise pilots to avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft.
“Furthermore, people living within valleys and along river/stream channels especially on the southeast, southwest and northwest sector of the edifice should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall should phreatic eruption occur,” furthered the agency.